This invention relates to polymers which exhibit release properties toward a wide variety of normally tacky and pressure-sensitive adhesive sheet materials.
For many years manufacturers of inherently tacky mastics or adhesives have protected the compositions with such anti-stick, or "abhesive" material as wax-coated paper, plastic films, plastic-coated paper, starch-impregnated fabrics, and extremely complex polymer systems. The last-named type of polymer has found particular application as a coating on the back surface of normally tacky and pressure-sensitive adhesive tape wound in roll form, where it functions as a so-called low adhesion backsize (LAB), facilitating use of the tape and preventing inadvertent transfer of the adhesive to the back surface. The force to separate the tape from an LAB coating typically ranges from 150 to 900 grams per inch of width, lower values generally causing roll instability and handling problems, and higher values making it excessively difficult to use the tape. For exemplary polymeric low adhesion backsizes, see U.S. Pat. Nos. 2,532,011, 2,607,711, 2,876,894, 3,318,852, and 3,342,625.
For some products, e.g., labels or large adhesive-coated sheets sold in other than roll form, it is desirable to have a protective release liner to which normally tacky and pressure-sensitive adhesives adhere very weakly; U.S. Pat. Nos. 3,230,289, 3,565,750, and 3,729,444 are illustrative of such products, all of which are based on a silicone coating of some type. The force to separate a pressure-sensitive adhesive from a silicone-treated surface is typically in the range of 10 to 40 grams per inch of width, usually much too low for use as a low adhesion backsize. Generally speaking, it has previously been almost impossible to obtain materials having release properties intermediate those of the LAB-type polymers and those of the silicones without sacrificing some other essential property.
Recognizing the desirability of a release coating having properties intermediate the 40 grams per inch shown by the extremely expensive silicones and the 600 grams per inch shown by more modestly priced typical low adhesion backsizes, attempts have been made to modify the silicone polymers by blending or reacting them with other less effective release materials; see, e.g., U.S. Pat. Nos. 3,328,482, 3,723,566, and 3,770,687. Some of the resultant modifications so contaminate a pressure-sensitive adhesive that it loses its tack, while others gradually react with a pressure-sensitive adhesive in such a manner that they cannot be separated after aging. Other compositions are difficult to reproduce with consistency, exhibit changed release properties as the silicone gradually migrates to the surface, require cure temperatures so high that they adversely affect the substrate on which they are coated, or are effective only with a few specific adhesives.